Extend battery life on USB nano to 2-4x

[CT_]

I got my USB nano pump and like all things the first thing I did was take it apart.  I was surprised to find this 51 ohm resistor in parallel with the pump.  (I also recognized the motor/pump under the silicone sleeve as one I already had several of for another project.  oops!)

I noodled over why that was there some tonight, and I think its because the pump doesn't sink enough current to be detected by most USB battery banks.  Without the resistor most power packs will auto-shutoff.  If you're running two or more off the same battery or have a USB "UPS" instead of battery bank you really don't need this resistor and can clip this resistor off to get about 2.5x more battery life (when fully loaded, more if there's not much air restriction) off of a battery backup.  You can also clip the resistor if you just want to save 1/2 watt of power consumption.

 

Some googling also turned up the little known feature of /some/ usb battery banks.  If you turn it on and hold the button for 3s it won't auto shut off.  I tried it on my battery bank with no success so YMMV. 

 

 

[Fish Folk]

6 hours ago, CT_ said:

 

I got my USB nano pump and like all things the first thing I did was take it apart.  I

 

Interesting! I promise I won’t be tearing mine apart. But this nerm loves to learm,  so thanks for sharing. “Jailbreaking” stuff does scratch that incipient DIY itch every hobbyist gets. 

[Socqua]

I watched this video awhile back before I ordered my USB nano pump, and I think he says the same thing you're saying: that you can change that resistor to 1) draw less power (conserve energy) and 2) last longer on battery. Assuming your battery backup still detects a power draw.

 

[TheDukeAnumber1]

I wonder if anyone has tried to replace the resistor with a big enough cap or just put a cap in series to get the best of both worlds. May test myself.

[Ben_RF]

This is one awesome post! Thank you! I love post like this.

[Socqua]

Hmm I'll have to think about this more, but I don't think a capacitor is going to give you the best of both worlds. In parallel it's just going to reduce the noise on the line, I think. And in either series or parallel it's not going to draw enough extra current to mimic what the resistor is doing here (drawing extra current, converting to heat, and keeping the dumb USB charger from thinking the system is off). Unless you mean a really, really huge cap.

I'm probably wrong or misread your response @TheDukeAnumber1 so feel free to correct me.

[TheDukeAnumber1]

55 minutes ago, Socqua said:

Hmm I'll have to think about this more, but I don't think a capacitor is going to give you the best of both worlds. In parallel it's just going to reduce the noise on the line, I think. And in either series or parallel it's not going to draw enough extra current to mimic what the resistor is doing here (drawing extra current, converting to heat, and keeping the dumb USB charger from thinking the system is off). Unless you mean a really, really huge cap.

I'm probably wrong or misread your response @TheDukeAnumber1 so feel free to correct me.

I figured a cap big enough to do anything meaningful would change the form factor quite a bit. I was thinking a cap big enough to wake up the power bank and hopefully it stays on once the cap stops drawing power, or maybe it would create a situation where the bank would shutoff, the cap drains into the motor or resistor, then the bank restarts. Power supplies can be so all over the place in specs and quality, at least in my experience. Might be worth a test, I'm open to being wrong here though.

[Socqua]

1 hour ago, TheDukeAnumber1 said:

I figured a cap big enough to do anything meaningful would change the form factor quite a bit. I was thinking a cap big enough to wake up the power bank and hopefully it stays on once the cap stops drawing power, or maybe it would create a situation where the bank would shutoff, the cap drains into the motor or resistor, then the bank restarts. Power supplies can be so all over the place in specs and quality, at least in my experience. Might be worth a test, I'm open to being wrong here though.

Ahh I see what you're saying now. I think the battery bank would turn on to charge the cap initially, eventually the cap would fill, the power bank would detect low current and shutoff. The cap would then drain to run the motor, eventually need to be recharged, which would kick the power bank back on. Rinse and repeat, cycling the power bank on and off. Probably would end up being more efficient than the resistor, but might shorten the life of your pump?

There's not much that isn't worth experimenting. In my experience you can only learn so much on paper. So do let us know how it goes if you open one up!

[CT_]

I did see someone make a circuit to periodically draw higher current to keep the battery bank awake.  It ran at 2% duty so that lowers wasted power from 500mW to 1mW.

 

If you're comfortable with electronics I think the best solution is to double the current sense resistor in your battery bank.  Cheap and easy.